A method is described for determining the oil yield from a combustion retort using only the capillary column chromotogram of the oil. The heating rate and/or retorting temperature and the resulting yield loss by oil coking is determined from the 1-alkene/n-alkane ratios. The amount of combustion and associated cracking is determined from naphthalene/straight-chain hydrocarbon ratios. The utility of this method is demonstrated using oil samples from several large-scale retorting operations. The possibility of using the oil mist from an in-situ retort for an on-line determination of the current retort performance is discussed.